During the last decade, the use of N-heterocyclic carbenes (NHCs) as ligands in organometallic complexes has become routine. NHCs, as neutral, two-electron donors with little backbonding character, have replaced phosphines in a variety of applications. See Diez-Gonzalez, S.; Nolan, S. P. Coord. Chem. Rev. 2007, 251, 874; Herrmann, W. A., Angew. Chem., Int. Ed. 2002, 41, 1290. Particularly, their use as ligands in ruthenium-based olefin metathesis has allowed for great gains in both activity and stability. Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999, 1, 953. There is also increasing interest in NHCs as nucleophilic reagents and organocatalysts, with wide use in condensation reactions such as the benzoin condensation, among others. Marion, N.; Diez-Gonzalez, S.; Nolan, S. P. Angew. Chem., Int. Ed. 2007, 46, 2988.
Because saturated free carbenes are sensitive toward oxygen and moisture, they are, in most applications, prepared in situ via the deprotonation of their corresponding imidazol(in)ium salts (Equation 1, where the R groups refer to alkyl and aryl groups known in the art for NHC ligands). Therefore, facile and high yielding methods for the synthesis of imidazol(in)ium salts are of great interest.

The synthesis of unsaturated imidazolium salts has been optimized and they are now easily prepared by a one step procedure starting from glyoxal, substituted aniline, formaldehyde and an acid. Arduengo, A. J., III, Preparation of 1,3-Disubstitutedlmidazolium Salts, 1991, U.S. Pat. No. 5,077,414. Unfortunately, the preparation of saturated imidazolinium salts still requires several synthetic transformations, including either a palladium-catalyzed C—N coupling or a reduction (Equation 2, where the R groups refer to the hydrocarbyl, or substituted hydrocarbyl groups in U.S. Pat. No. 5,077,414).

A new pathway to prepare unsaturated imidazolinium salts was developed starting from the addition of a compound featuring two leaving groups to lithiated formamidines. Jazzar, R; Liang, H; Donnadieu, B; Bertrand, G. Journal of Organometallic Chemistry 2006, 691 3201. However, the cyclization reaction of the formanidine to the final imidazolinium requires an additional reflux in THF (Equation 3).

There remains a need in the art to provide improved methods for the preparation of saturated imidazolinium salts and similar compounds from commercially available substituted anilines, naphthylamines, or anthracenylamines. This invention answers that need.